This invention relates a method and an apparatus for aligning a waveguide with a radiation source, and more particularly, to a method an apparatus for aligning a waveguide with a radiation source using photoluminescence induced in the waveguide by the radiation source.
Many processes involving optical waveguides require a precise alignment between an optical waveguide and a radiation beam. For example, in Bragg grating writing by flood exposure, an ultraviolet (UV) laser light interference pattern is used to write the grating in a core of an optical fiber. The interference pattern, which is typically focussed, needs to be precisely aligned with the core. If the core receives light from a part of the interference pattern outside of the focus, the intensity of the interference pattern will not be maximal and an exposure time to the beam required to write a given Bragg grating will be increased with respect to the exposure time that would be required if the core was at the focus of the interference pattern. In addition, if no monitoring of the Bragg grating writing process can be performed during the writing phase, the absence of a well-controlled interference pattern intensity may lead to a Bragg grating into which index of refraction variations are not large enough to provide a required grating performance.
The photoluminescence of several materials used to manufacture optical fibers and other optical waveguides can be used to align the optical fiber with a laser beam in preparation for Bragg grating writing. Once the optical fiber is properly aligned, the laser beam is replaced by the interference pattern and the Bragg grating writing process can be performed.
Typically, an ultraviolet (UV) laser is held immobile and produces the laser beam. A supporting member supports the optical fiber, the longitudinal axis of the optical fiber being perpendicular to the longitudinal axis of the laser beam. The supporting member is mobile in a direction perpendicular to the longitudinal axis of the optical fiber and perpendicular to the longitudinal axis of the laser beam. The supporting member can be displaced either manually or with a motorized actuator.
When a portion of the laser beam illuminates the photoluminescent core of the optical fiber, the light produced by photoluminescence is propagated through the optical fiber to its extremities. A power meter located at one extremity of the fiber can then measure the intensity of the photoluminescence light, which depends on the power carried by the portion of the laser beam illuminating the core of the optical fiber. Accordingly, when the focus of the laser beam is centered on the core of the optical fiber, the intensity of the photoluminescence measured at the power meter is maximal. Therefore, to center the optical fiber on the laser beam, the supporting member is displaced to achieve a maximal value of the intensity of the photoluminescence detected at the extremity of the optical fiber.
The method described above requires that the power meter block one extremity of the optical fiber. In some instances, this is undesirable as it could be advantageous to have other equipment, such as Bragg grating writing monitoring equipment, connected to the extremities of the optical fiber.
Against this background, there exists a need to provide novel methods and devices for aligning a waveguide with a radiation source.
In accordance with a broad aspect, the invention provides and apparatus for aligning an optical waveguide with a radiation source. The waveguide has a longitudinal axis that defines a main optical propagation path and the radiation source illuminates the waveguide such that the waveguide generates light via photoluminescence. At least a portion of the light generated via photoluminescence is emitted from the waveguide along a direction generally transverse to the longitudinal axis. The apparatus includes a sensor responsive to the light emitted from the waveguide along a direction generally transverse to the longitudinal axis for producing an output signal. Alignment means then vary the alignment of the radiation source and the waveguide at least partly in dependence of the output signal.
Advantageously, the invention allows aligning an optical waveguide with a radiation source, such as a laser, by using light generated through photoluminescence and emitted along a direction generally transverse to the longitudinal axis of the waveguide. By using photoluminescence emitted transversely to the longitudinal axis of the waveguide rather than detecting photoluminescence emitted at an extremity of the optical waveguide, the extremities of the optical waveguide remain free and can therefore by used for other useful purposes such as signal analysis.
In a specific example of implementation, the output signal generated by the sensor is an intensity signal indicative of an intensity of light. In a specific example of implementation, the alignment means includes a controller module responsive to the intensity signal for causing the alignment of the radiation source and the waveguide to be varied.
In a first non-limiting implementation, the controller module causes the waveguide to be displaced in order to cause the alignment of the radiation source and the waveguide to be varied.
In a second non-limiting implementation, the controller module causes the radiation source to be displaced in order to cause the alignment of the radiation source and the waveguide to be varied.
In a non-limiting implementation, the alignment means further comprise a light reflecting member positioned such as to redirect a radiation beam emitted by the radiation source. The reflecting member may be any suitable component adapted to reflect a radiation beam. A specific example of a light reflecting member is a mirror. In a specific non-limiting implementation, the light reflecting member is in the form of a mirror. The controller module is operative to cause the light reflecting member to be displaced in order to cause the alignment of the radiation source and the waveguide to be varied.
The controller module generates a control signal at least in part on the basis of the intensity signal. An actuator, responsive to the control signal generated by the controller module, displaces the light reflecting member such as to vary the alignment of the radiation source and the waveguide at least in part on the basis of the control signal. The displacing of the light reflecting member may be effected by means of rotation, by means of translation or by a combination of the translation and rotation of the light reflecting member.
In accordance with another broad aspect, the invention provides a method for aligning an optical waveguide with a radiation source, the waveguide having a longitudinal axis that defines a main optical propagation path. The method includes illuminating the waveguide such that the waveguide generates light via photoluminescence, at least a portion of the light generated via photoluminescence being emitted from the waveguide along a direction generally transverse to the longitudinal axis. An output signal is generated at least in part on the basis of light emitted from the waveguide along a direction generally transverse to the longitudinal axis. The alignment of the radiation source and the waveguide is then varied at least partly in dependence of the output signal.
In accordance with another broad aspect, the invention provides an apparatus for aligning an optical waveguide with a radiation source. The apparatus includes a waveguide support member, a sensor and a controller module. The waveguide support member is for holding an optical waveguide, the waveguide having a longitudinal axis that defines a main optical propagation path. The radiation source illuminates the waveguide such that the waveguide generates light via photoluminescence, at least a portion of the light generated via photoluminescence being emitted from the waveguide along a direction generally transverse to the longitudinal axis. The sensor is positioned in proximity to the optical waveguide and is responsive to the light emitted from the waveguide along a direction generally transverse to the longitudinal axis to produce an intensity signal indicative of a measure of the light detected. The controller module is responsive to the intensity signal for causing the alignment of the radiation source and the waveguide to be varied at least partly in dependence of the intensity signal.
In a first specific example of implementation, the waveguide support member is moveable and the controller module is responsive to the intensity signal for causing the waveguide support member to be displaced such as to cause the alignment of the radiation source and the waveguide to be varied.
In a first specific example of implementation, the controller module is responsive to the intensity signal for causing the direction of the radiation beam emitted by the radiation source to be altered such that the alignment of the radiation source and the waveguide to be varied.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.